1,720,968 research outputs found
Acoustic characterization of automotive mufflers. Part II: validation of the numerical models by means of experimental data
No full textIncreasing interest is being paid to noise pollution of internal combustion engines and as a result, recent international standards imposed more severe limitations to acoustic emissions on engine manufacturers. In particular, the noise coming from gas-dynamic interactions has an important influence in determining the final noise level of the engine; as a consequence, the muffler design is currently being considered as one of the most important research threads for engine companies. Within this context, the 1D approach to numerical simulations, which has been successfully applied by industrial designers to the fluid-dynamic design of the engine, is considered to be inaccurate in the evaluation of the acoustic behavior of the muffler for medium-high frequencies. On the other hand, an extension of the applicability of these codes in the medium-high frequencies would be desirable. The direct advantage would be the use of the same software for the simulation of both the fluid-dynamic and acoustic performance of the engine.On these bases, a commercial 1D numerical code was primarily analyzed in terms of accuracy, computational cost and modeling capability of mufflers from the acoustic point of view. As a second step, two non-conventional approaches were developed in order to improve the prediction capabilities of the 1D code and to widen its frequency range of validity, as well. The base scheme of these new approaches was to extend the application of the traditional 1D nonlinear equations not only in the axial direction but also in perpendicular directions within the cross-section of the muffler, achieving a simplified description of the acoustic phenomena in the whole volume.The 1D predictions using these new approaches were compared both with several sets of experimental data collected on a purposefully developed test rig and specific 3D simulations; as a result, their limits in terms of accuracy were highlighted. Moreover, the introduction of the new sub-models increased the accuracy of the simulations and the frequency range of validity, leading to notable results with respect to traditional formulations of the problem
Acoustic characterization of automotive mufflers. Part I: test rig design and evaluation of acoustic properties
No full textIn current automotive research, increasing attention is being paid to the design of mufflers due to the lower noise levels which have been established by the acoustic international standards. The traditional design approaches are no longer sufficient to meet the standards and more refined techniques are necessary.Within this context, a specific test rig was built at the Energy Engineering Department of the University of Florence to analyze the acoustic characteristics of both industrial mufflers and simplified models. In particular, the latter is commonly used to investigate in detail the physical phenomena connected to the acoustic response of these disposals and to calibrate numerical models. The test rig operates at ambient condition with no flow. Instead of the widely used Four Microphones Technique, the test rig was designed considering the Multi-Microphone Technique, which guarantees a wider reliable frequency range of analysis and lower errors in the evaluation of the acoustic properties of mufflers. In this paper the details of the criteria adopted in the design and the characterization of the test rig will be discussed in depth
Gallbladder volume variations after meal ingestion
No full textObjective: To assess gallbladder (GB) volume variations in response to a standard meal.
Methods: We assessed these variations with ultrasonography at brief intervals over the postprandial period, which included the emptying and refilling phases of the GB.
Results: During both emptying and refilling of the GB, the volume fluctuated continuously, with brief alternating volume decrements and increments. The phases of emptying and refilling appear to be the net result of the algebraic sum of these volume fluctuations. In the emptying phase, the volume decrements showed a greater volume (35.7 +/- 10.7 ml vs. 14.8 +/- 8.4 ml) and lasted longer (158 +/- 37 min vs. 85 +/- 44 min) than the volume increments, whereas the opposite took place in the refilling phase (4.3 +/- 3.4 ml vs. 16.4 +/- 12.2 ml; 39 +/- 20 min vs. 84 +/- 37 min).
Conclusion: It is probable that the continuous GB volume fluctuations are the expression of hepatic bile recycling in the GB during the entire postprandial period, and the amount of bile recycled by the GB is greater during the emptying than the refilling phase
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
